1. Field of the Invention
The present invention relates to an X-ray imaging device in which the scintillator for converting an X-ray into a visible light, or the like and the imaging devices for receiving the visible light, or the like are used in combination and, more particularly, a resolution-variable X-ray imaging device whose resolution can be changed as occasion demands and an X-ray CT apparatus using the same.
2. Description of Related Art
As the X-ray imaging device for capturing an image by visualizing an X-ray, there are some devices that can sense directly an X-ray and others that can visualize an X-ray by using the scintillator and then capture an image by using the imaging device such as CCD, or the like, as set forth in JP-A-5-152597, JP-A-6-214036, JP-A-11-151235, JP-A-2000-56028 and JP-A-2003-17676.
When the X-ray (computed tomography) CT apparatus shown in FIG. 10, for example, is constructed by using the scintillator and the imaging device in combination, a circular opening portion 104 into which a subject 103 on a stretcher 102 is carried is provided to a center of a main body of an X-ray CT apparatus 101. An X-ray irradiator 105 for irradiating an X-ray onto the subject 103, an X-ray imaging device (having a scintillator and an imaging device) 106 for receiving the X-ray transmitted through the subject 103, a driving mechanism (not shown) for causing the X-ray irradiator 105 and the X-ray imaging device 106 to turn integrally around the circular opening portion 104, and a transfer unit 107 for transferring the captured image of the subject 103 output from the X-ray imaging device 106 to the outside are provided to the main body of the X-ray CT apparatus 101.
FIG. 11 is a schematic plan view of the X-ray imaging device 106 in the related art. A great number of pixels 109 having a same size are aligned and formed vertically and horizontally at a same pitch respectively on the substrate. Each pixel 109 is constructed by a photodiode 110 formed on the semiconductor substrate, and a signal reading circuit consisting of a reset transistor, FDA, and a reading transistor, which are formed in positions adjacent to this photodiode 110.
The signal reading circuit of each pixel 109 outputs a sensed signal responding to a signal charge stored in the photodiode 110 of the pixel 109 to an output signal line when it is designated by a vertical shift register 111 and a horizontal shift register 112. Then, this sensed signal is output from the X-ray imaging device 106 to the transfer unit 107.
In the X-ray imaging device 106 in the related art, as shown in FIG. 11, since a great number of pixels having the same shape are aligned and formed on the substrate at same pitches, a resolution of the image is fixed basically. That is, the tomogram is captured at the same resolution, no matter which part of the subject 103 the X-ray imaging device 106 is captured.
It is preferable that the X-ray CT apparatus should have a high-resolution X-ray imaging device 106, a driving mechanism and a signal processing mechanism that can be operated at a high scanning rate. In this case, such X-ray CT apparatus becomes inevitably expensive (JP-A-2002-200073, JP-A-5-269122 and JP-A-2002-306467).
With the technical progress in recent years, a resolution of the X-ray imaging device used in the X-ray CT apparatus is increased and also a scanning rate is increased to a higher rate. However, in the configuration of the X-ray imaging device in the related art, even when a portion of the subject whose image needs merely a low resolution is invested, the resolution-fixed imaging device is used to capture the image. Therefore, the image of the corresponding portion of the subject is captured at an excessively high resolution as image data.
If data acquisition at a lower resolution may be allowed, the image data can be acquired at a higher scanning rate correspondingly, and thus an exposure dose of the subject can be reduced. However, the resolution is fixed in the X-ray imaging device in the related art, it is impossible for the user's operation to increase a scanning rate while keeping a low resolution of the image.